Cylinder liner assemblies used in large diesel engines include water passages coupled to a head. The head is secured to the liner assembly by several studs which are fastened to the liner. The liner has a threaded hole to receive a threaded end section of each stud. To assure that the studs remain securely fastened to the liner so that the stud does not move when a nut is applied or removed from the outer end, an interference fit is used in the threaded connection. Also, to prevent the leakage around the stud of water entering the threaded hole through porous liner walls, full thread engagement of the outer threads with the hole is required. The ANSI standard B1.12 "Class 5 Interference-Fit Thread" sets forth the standard specifications for such studs.
When using the standard studs with rolled threads, it was found that the interference fit caused spalling believed to be due to welding of the interface surfaces as a result of high frictional forces. The friction is caused by the geometric interference, micro finish of the mating threads, and debris trapped between the mating threads during installation. During installation of a class 5 thread, material is shaved off or spalls off the mating threads and becomes trapped in the thread interface. This trapped debris increases the thread interference and gouges the threads creating larger balled up debris. If the debris acquires sufficient size, the friction and driving torque increase until failure occurs. The installation of the standard studs was marked by high torque and failures such as stripping the thread form on both the male and female mating members, cracking of the female threaded member due to excessive hoop stress, torsional failure of the fastener through the minor diameter of the thread form, and stalling of the fastener before the fastener is driven to the proper depth.